I don't think I've ever commuted on a 'commuter bike', with the exception of three days using a bike share at an out of town conference (not sure if that's a commuter bike). I'm thinking of a 'commuter bike' as what's typically marketed that way: an upright, flat bar bicycle with clearance for wider tires than a road bike and braze-ons for attaching racks, fenders, etc.
Why I don't use a 'commuter bike':
- Upright position and lack of hand positions is less comfortable to me
- I prefer to have a lighter bike and carry things on my back, rather an overbuilt bike with a rack
- Narrow tires are fine for my commutes, except in ice - which can be accommodated with a gravel bike
- I like to integrate recreational road cycling and commutes into the same ride
- Deep winter riding is better served by an old MTB with wider studded tires than a commuter bike (and 26x2.0 tires are still readily available.)